package com.nulldev.util.web.HttpServer3.util;

import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.SocketException;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;

import com.nulldev.util.VariableAPI.ByteUtil;
import com.nulldev.util.io.IOUtils;

/**
 * BetterBufferedInputStream.
 * 
 * Features: - Allows cache-size change. That's it really.
 */
public class BetterBufferedInputStream extends FilterInputStream {

	private static int DEFAULT_BUFFER_SIZE = IOUtils.MEMORY_ALLOC_BUFFER;

	/**
	 * The maximum size of array to allocate. Some VMs reserve some header words in
	 * an array. Attempts to allocate larger arrays may result in OutOfMemoryError:
	 * Requested array size exceeds VM limit
	 */
	private static int MAX_BUFFER_SIZE = Integer.MAX_VALUE - 8;

	/**
	 * The internal buffer array where the data is stored. When necessary, it may be
	 * replaced by another array of a different size.
	 */
	protected volatile byte buf[];

	/**
	 * Atomic updater to provide compareAndSet for buf. This is necessary because
	 * closes can be asynchronous. We use nullness of buf[] as primary indicator
	 * that this stream is closed. (The "in" field is also nulled out on close.)
	 */
	private static final AtomicReferenceFieldUpdater<BetterBufferedInputStream, byte[]> bufUpdater = AtomicReferenceFieldUpdater
			.newUpdater(BetterBufferedInputStream.class, byte[].class, "buf");

	/**
	 * The index one greater than the index of the last valid byte in the buffer.
	 * This value is always in the range <code>0</code> through
	 * <code>buf.length</code>; elements <code>buf[0]</code> through
	 * <code>buf[count-1]
	 * </code>contain buffered input data obtained from the underlying input stream.
	 */
	protected volatile int count;

	/**
	 * The current position in the buffer. This is the index of the next character
	 * to be read from the <code>buf</code> array.
	 * <p>
	 * This value is always in the range <code>0</code> through <code>count</code>.
	 * If it is less than <code>count</code>, then <code>buf[pos]</code> is the next
	 * byte to be supplied as input; if it is equal to <code>count</code>, then the
	 * next <code>read</code> or <code>skip</code> operation will require more bytes
	 * to be read from the contained input stream.
	 *
	 * @see java.io.BufferedInputStream#buf
	 */
	protected volatile int pos;

	/**
	 * The value of the <code>pos</code> field at the time the last
	 * <code>mark</code> method was called.
	 * <p>
	 * This value is always in the range <code>-1</code> through <code>pos</code>.
	 * If there is no marked position in the input stream, this field is
	 * <code>-1</code>. If there is a marked position in the input stream, then
	 * <code>buf[markpos]</code> is the first byte to be supplied as input after a
	 * <code>reset</code> operation. If <code>markpos</code> is not <code>-1</code>,
	 * then all bytes from positions <code>buf[markpos]</code> through
	 * <code>buf[pos-1]</code> must remain in the buffer array (though they may be
	 * moved to another place in the buffer array, with suitable adjustments to the
	 * values of <code>count</code>, <code>pos</code>, and <code>markpos</code>);
	 * they may not be discarded unless and until the difference between
	 * <code>pos</code> and <code>markpos</code> exceeds <code>marklimit</code>.
	 *
	 * @see java.io.BufferedInputStream#mark(int)
	 * @see java.io.BufferedInputStream#pos
	 */
	protected volatile int markpos = -1;

	/**
	 * The maximum read ahead allowed after a call to the <code>mark</code> method
	 * before subsequent calls to the <code>reset</code> method fail. Whenever the
	 * difference between <code>pos</code> and <code>markpos</code> exceeds
	 * <code>marklimit</code>, then the mark may be dropped by setting
	 * <code>markpos</code> to <code>-1</code>.
	 *
	 * @see java.io.BufferedInputStream#mark(int)
	 * @see java.io.BufferedInputStream#reset()
	 */
	protected volatile int marklimit;

	/**
	 * Check to make sure that underlying input stream has not been nulled out due
	 * to close; if not return it;
	 */
	private InputStream getInIfOpen() throws IOException {
		InputStream input = in;
		if (input == null)
			throw new IOException("Stream closed");
		return input;
	}

	/**
	 * Check to make sure that buffer has not been nulled out due to close; if not
	 * return it;
	 */
	private byte[] getBufIfOpen() throws IOException {
		byte[] buffer = buf;
		if (buffer == null)
			throw new IOException("Stream closed");
		return buffer;
	}

	/**
	 * Creates a <code>BufferedInputStream</code> and saves its argument, the input
	 * stream <code>in</code>, for later use. An internal buffer array is created
	 * and stored in <code>buf</code>.
	 *
	 * @param in the underlying input stream.
	 */
	public BetterBufferedInputStream(InputStream in) {
		this(in, DEFAULT_BUFFER_SIZE);
	}

	/**
	 * Creates a <code>BufferedInputStream</code> with the specified buffer size,
	 * and saves its argument, the input stream <code>in</code>, for later use. An
	 * internal buffer array of length <code>size</code> is created and stored in
	 * <code>buf</code>.
	 *
	 * @param in   the underlying input stream.
	 * @param size the buffer size.
	 * @exception IllegalArgumentException if {@code size <= 0}.
	 */
	public BetterBufferedInputStream(InputStream in, int size) {
		super(in);
		if (size <= 0) {
			throw new IllegalArgumentException("Buffer size <= 0");
		}
		buf = new byte[size];
	}

	/**
	 * Fills the buffer with more data, taking into account shuffling and other
	 * tricks for dealing with marks. Assumes that it is being called by a
	 * synchronized method. This method also assumes that all data has already been
	 * read in, hence pos > count.
	 */
	private void fill() throws IOException {
		byte[] buffer = getBufIfOpen();
		if (markpos < 0)
			pos = 0; /* no mark: throw away the buffer */
		else if (pos >= buffer.length) /* no room left in buffer */
			if (markpos > 0) { /* can throw away early part of the buffer */
				int sz = pos - markpos;
				System.arraycopy(buffer, markpos, buffer, 0, sz);
				pos = sz;
				markpos = 0;
			} else if (buffer.length >= marklimit) {
				markpos = -1; /* buffer got too big, invalidate mark */
				pos = 0; /* drop buffer contents */
			} else if (buffer.length >= MAX_BUFFER_SIZE) {
				throw new OutOfMemoryError("Required array size too large");
			} else { /* grow buffer */
				int nsz = (pos <= MAX_BUFFER_SIZE - pos) ? pos * 2 : MAX_BUFFER_SIZE;
				if (nsz > marklimit)
					nsz = marklimit;
				byte nbuf[] = new byte[nsz];
				System.arraycopy(buffer, 0, nbuf, 0, pos);
				if (!bufUpdater.compareAndSet(this, buffer, nbuf)) {
					// Can't replace buf if there was an async close.
					// Note: This would need to be changed if fill()
					// is ever made accessible to multiple threads.
					// But for now, the only way CAS can fail is via close.
					// assert buf == null;
					throw new IOException("Stream closed");
				}
				buffer = nbuf;
			}
		count = pos;
		int n = getInIfOpen().read(buffer, pos, buffer.length - pos);
		if (n > 0)
			count = n + pos;
	}

	/**
	 * See the general contract of the <code>read</code> method of
	 * <code>InputStream</code>.
	 *
	 * @return the next byte of data, or <code>-1</code> if the end of the stream is
	 *         reached.
	 * @exception IOException if this input stream has been closed by invoking its
	 *                        {@link #close()} method, or an I/O error occurs.
	 * @see java.io.FilterInputStream#in
	 */
	public synchronized int read() throws IOException {
		if (pos >= count) {
			try {
				fill();
			} catch (SocketException f) {
				if (f != null && f.getMessage().contains("Socket closed"))
					return -1;
				throw f;
			} catch (IOException e) {
				throw e;
			}
			if (pos >= count)
				return -1;
		}
		return getBufIfOpen()[pos++] & 0xff;
	}

	/**
	 * Read characters into a portion of an array, reading from the underlying
	 * stream at most once if necessary.
	 */
	private int read1(byte[] b, int off, int len) throws IOException {
		int avail = count - pos;
		if (avail <= 0) {
			/*
			 * If the requested length is at least as large as the buffer, and if there is
			 * no mark/reset activity, do not bother to copy the bytes into the local
			 * buffer. In this way buffered streams will cascade harmlessly.
			 */
			if (len >= getBufIfOpen().length && markpos < 0) {
				return getInIfOpen().read(b, off, len);
			}
			fill();
			avail = count - pos;
			if (avail <= 0)
				return -1;
		}
		int cnt = (avail < len) ? avail : len;
		System.arraycopy(getBufIfOpen(), pos, b, off, cnt);
		pos += cnt;
		return cnt;
	}

	/**
	 * Reads bytes from this byte-input stream into the specified byte array,
	 * starting at the given offset.
	 *
	 * <p>
	 * This method implements the general contract of the corresponding
	 * <code>{@link InputStream#read(byte[], int, int) read}</code> method of the
	 * <code>{@link InputStream}</code> class. As an additional convenience, it
	 * attempts to read as many bytes as possible by repeatedly invoking the
	 * <code>read</code> method of the underlying stream. This iterated
	 * <code>read</code> continues until one of the following conditions becomes
	 * true:
	 * <ul>
	 *
	 * <li>The specified number of bytes have been read,
	 *
	 * <li>The <code>read</code> method of the underlying stream returns
	 * <code>-1</code>, indicating end-of-file, or
	 *
	 * <li>The <code>available</code> method of the underlying stream returns zero,
	 * indicating that further input requests would block.
	 *
	 * </ul>
	 * If the first <code>read</code> on the underlying stream returns
	 * <code>-1</code> to indicate end-of-file then this method returns
	 * <code>-1</code>. Otherwise this method returns the number of bytes actually
	 * read.
	 *
	 * <p>
	 * Subclasses of this class are encouraged, but not required, to attempt to read
	 * as many bytes as possible in the same fashion.
	 *
	 * @param b   destination buffer.
	 * @param off offset at which to start storing bytes.
	 * @param len maximum number of bytes to read.
	 * @return the number of bytes read, or <code>-1</code> if the end of the stream
	 *         has been reached.
	 * @exception IOException if this input stream has been closed by invoking its
	 *                        {@link #close()} method, or an I/O error occurs.
	 */
	public synchronized int read(byte b[], int off, int len) throws IOException {
		getBufIfOpen(); // Check for closed stream
		if ((off | len | (off + len) | (b.length - (off + len))) < 0) {
			throw new IndexOutOfBoundsException();
		} else if (len == 0) {
			return 0;
		}

		int n = 0;
		for (;;) {
			int nread = read1(b, off + n, len - n);
			if (nread <= 0)
				return (n == 0) ? nread : n;
			n += nread;
			if (n >= len)
				return n;
			// if not closed but no bytes available, return
			InputStream input = in;
			if (input != null && input.available() <= 0)
				return n;
		}
	}

	@Override
	public int read(byte[] b) throws IOException {
		return this.read(b, 0, b.length);
	}

	/**
	 * See the general contract of the <code>skip</code> method of
	 * <code>InputStream</code>.
	 *
	 * @exception IOException if the stream does not support seek, or if this input
	 *                        stream has been closed by invoking its
	 *                        {@link #close()} method, or an I/O error occurs.
	 */
	public synchronized long skip(long n) throws IOException {
		getBufIfOpen(); // Check for closed stream
		if (n <= 0) {
			return 0;
		}
		long avail = count - pos;

		if (avail <= 0) {
			// If no mark position set then don't keep in buffer
			if (markpos < 0)
				return getInIfOpen().skip(n);

			// Fill in buffer to save bytes for reset
			fill();
			avail = count - pos;
			if (avail <= 0)
				return 0;
		}

		long skipped = (avail < n) ? avail : n;
		pos += skipped;
		return skipped;
	}

	/**
	 * Returns an estimate of the number of bytes that can be read (or skipped over)
	 * from this input stream without blocking by the next invocation of a method
	 * for this input stream. The next invocation might be the same thread or
	 * another thread. A single read or skip of this many bytes will not block, but
	 * may read or skip fewer bytes.
	 * <p>
	 * This method returns the sum of the number of bytes remaining to be read in
	 * the buffer (<code>count&nbsp;- pos</code>) and the result of calling the
	 * {@link java.io.FilterInputStream#in in}.available().
	 *
	 * @return an estimate of the number of bytes that can be read (or skipped over)
	 *         from this input stream without blocking.
	 * @exception IOException if this input stream has been closed by invoking its
	 *                        {@link #close()} method, or an I/O error occurs.
	 */
	public synchronized int available() throws IOException {
		int n = count - pos;
		int avail = getInIfOpen().available();
		return n > (Integer.MAX_VALUE - avail) ? Integer.MAX_VALUE : n + avail;
	}

	/**
	 * See the general contract of the <code>mark</code> method of
	 * <code>InputStream</code>.
	 *
	 * @param readlimit the maximum limit of bytes that can be read before the mark
	 *                  position becomes invalid.
	 * @see java.io.BufferedInputStream#reset()
	 */
	public synchronized void mark(int readlimit) {
		marklimit = readlimit;
		markpos = pos;
	}

	/**
	 * See the general contract of the <code>reset</code> method of
	 * <code>InputStream</code>.
	 * <p>
	 * If <code>markpos</code> is <code>-1</code> (no mark has been set or the mark
	 * has been invalidated), an <code>IOException</code> is thrown. Otherwise,
	 * <code>pos</code> is set equal to <code>markpos</code>.
	 *
	 * @exception IOException if this stream has not been marked or, if the mark has
	 *                        been invalidated, or the stream has been closed by
	 *                        invoking its {@link #close()} method, or an I/O error
	 *                        occurs.
	 * @see java.io.BufferedInputStream#mark(int)
	 */
	public synchronized void reset() throws IOException {
		getBufIfOpen(); // Cause exception if closed
		if (markpos < 0)
			throw new IOException("Resetting to invalid mark");
		pos = markpos;
	}

	/**
	 * Tests if this input stream supports the <code>mark</code> and
	 * <code>reset</code> methods. The <code>markSupported</code> method of
	 * <code>BufferedInputStream</code> returns <code>true</code>.
	 *
	 * @return a <code>boolean</code> indicating if this stream type supports the
	 *         <code>mark</code> and <code>reset</code> methods.
	 * @see java.io.InputStream#mark(int)
	 * @see java.io.InputStream#reset()
	 */
	public boolean markSupported() {
		return true;
	}

	/**
	 * Closes this input stream and releases any system resources associated with
	 * the stream. Once the stream has been closed, further read(), available(),
	 * reset(), or skip() invocations will throw an IOException. Closing a
	 * previously closed stream has no effect.
	 *
	 * @exception IOException if an I/O error occurs.
	 */
	public void close() throws IOException {
		byte[] buffer;
		while ((buffer = buf) != null) {
			if (bufUpdater.compareAndSet(this, buffer, null)) {
				InputStream input = in;
				in = null;
				if (input != null)
					input.close();
				return;
			}
			// Else retry in case a new buf was CASed in fill()
		}
	}

	public void changeCacheSize(final int cacheSize) {
		if (cacheSize < 1)
			throw new UnsupportedOperationException("Invalid cache size: " + cacheSize);
		final byte[] old_cache = this.buf;
		this.buf = ByteUtil.concatenateByteArrays(old_cache, new byte[cacheSize - old_cache.length]);
	}
}
